From Fermi to W pairs - 65 years of the weak force
13 January 1999
On 16 January 1934, Enrico Fermi submitted for publication his famous paper on the first viable theory of the weak force, which is responsible for beta decay. In this paper*, he described the beta decay of a nucleus in terms of the creation and immediate emission of an electron simultaneously with an invisible neutrino. Fermi's theory, with some modifications, to this day provides a good description of beta decay, in which we see the weak force acting at low energies. But at higher energies Fermi's theory breaks down. A better theory of the weak force, which works at high energies, is in terms of a unified electroweak interaction, which requires additional particles to "carry" the weak force. Charged carriers, called W+ and W-, are responsible for processes such as beta decay. Today W particles are created and studied at high-energy particle accelerators such as the Large Electron Positron Collider (LEP) at CERN, the European Laboratory for Particle Physics. This week's image shows the probable decay of two W particles in the OPAL detector at LEP. Each W has decayed into two quarks (best known as the building bricks of protons and other particles), which materialise in the detector as four distinct sprays (or "jets") of particles. (You can see more images like this on the OPAL web pages.)
*(see E.Fermi, Zeitschrift fur Physik 88 161 (1934))
Credit: CERN/OPAL
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